The present invention relates to a therapy means comprising a blood pressure meter and a controller, and in particular to a therapy means for extracorporeal blood cleaning.
In various therapies, such as the hemodialysis, it is necessary to continuously monitor the patient""s blood pressure. For this purpose means for non-invasive blood pressure measurement are used, said means comprising a cuff which is placed around the patient""s arm, inflated and then slowly deflated with the blood pressure being measured. During this process the systolic and diastolic blood pressures are measured. To realize a quasi-continuous blood pressure measurement, measurements must be performed at intervals of a few minutes. In automatic blood pressure meters the cuff inflates automatically. During a therapy of several hours thus frequent repetitions of the described measuring process are required.
It is an object of the present invention to configure a therapy means, where blood pressure measurement at intervals is required, such that the number of measuring processes is reduced.
According to the present invention the blood pressure measurement is left undone at some of the times provided for this purpose and the measured values are substituted by hypothetical values gathered from a former blood pressure curve determined during a therapy undergone by the same patient.
Clinical experience with regard to dialysis patients have shown that the blood pressure curves of the patients lie within patient-specific scatter ranges during the dialysis treatment despite the intraindividual variabilty. If, after a first treatment period of e.g. 45 minutes, the current blood pressure curve is subjected to a statistical comparison with the stored curves determined during previous treatments of the same patient, a previous curve can be used as a basic curve whose values can be assumed as the actual blood pressure values. Thus a large portion of the presently required blood pressure measurements may become superfluous. In an initial phase the current blood pressure curve can be measured at short intervals of e.g. 5 minutes and compared with the stored blood pressure curves determined during previous treatments of the same patient. On the basis of statistical analyses and the relevant treatment parameters the previous blood pressure curve, which shows the largest similiarity to the current blood pressure curve, is determined from data storage and used as a basic curve for blood pressure control during the current treatment.
The present invention actively incorporates patient-specific experience regarding the blood pressure behaviour during previous treatments into the optimization of the current treatment. Depending on the course of the treatment the basic-curve method allows approximately 60% of the previously necessary blood pressure measurements taken on the patient to be omitted. The memory-based method does not require any additional measuring means or instruments. The required computation and memory capacities are small.
Preferably the controller, which controls, inter alia, the blood pressure measurement, carries out the following steps:
a) preparing and storing a collection of the time histories of the blood pressure determined during a plurality of therapy sessions to generate stored blood pressure curves and,
b) carrying out successive blood pressure measurements during a therapy session to obtain a current blood pressure curve,
c) determining, from the stored curves, as the basic curve a blood pressure curve which shows the largest similarity to the current blood pressure curve,
d) controlling the blood pressure utilizing values of the basic curve for the actual blood pressure value.
According to a preferred aspect of the present invention it is provided that subsequent to the utilization of values of the basic curve another measurement of the blood pressure is carried out, and the new measured value is used as the actual blood pressure value for control purposes. After the new measurement the previous blood pressure curve can be checked for similarity to the stored blood pressure curves to select a new basic curve, if necessary. Thus the statistical analysis can be repeated after each blood pressure measurement to select the optimum basic curve for the respective treatment phase.
According to a preferred aspect of the present invention it is provided that the extent of similarity of the previous blood pressure curve to a stored blood pressure curve decides upon the time interval up to the next measurement. For the similarity measurement statistical method can be used, such as the t test, the pattern-recognition method or the averaging method or combinations thereof. Each of these methods supplies a similarity value which e.g. increases with increasing similarity of the curves compared with each other. The extent of similarity is utilized according to the invention to define the interval between two blood pressure measurements.
The present invention is particularly suitable for dialyzers and other means for extracorporeal blood treatment, but also e.g. for the infusion therapy.